Martinique has three major marine ecosystems that are all undergoing a slow but continuous degradation: seagrass beds, mangroves, and coral reefs. It has a total of 294 square miles (473 km²) of reefs and lagoons, 12.4 square miles (20 km²) of mangroves, and 24.8 square miles (40 km²) of seagrass beds. Constructed reefs extend over a length of about 43 miles (70 km) and an area of ​​less than 124 square miles (200 km²). They are completely absent from the northwest coast of the island, where coral populations are, however, present from a depth of 32 ft (10 m). Seagrass beds and mangroves are less abundant there than on the eastern coast. The fringing reef is mostly developed on the southern and eastern shores of Martinique, while the barrier reef, of more algal than coral origin, is installed on the Atlantic coast and the non-bioconstructive coral beds are located near the very steep shores of the Caribbean coast, west of the island.